The First Picoseconds in Bacterial Photosynthesis—Ultrafast Electron Transfer for the Efficient Conversion of Light Energy

Zinth, Wolfgang; Wachtveitl, Josef

doi:10.1002/cphc.200400458

Cited by 190 publications

(235 citation statements)

References 132 publications

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“…Photochemistry Initiated from P. Following excitation of P, the consensus view is that BChl A functions as the initial electron acceptor for P*, forming the P þ BChl A − transient state with a 3 ps risetime (room temperature), but is rapidly converted by electron transfer to BPh A with a 0.9 ps time constant (7). However the overlap of the ground and excited-state optical absorptions of the cofactors has posed challenges for easy verification of this reaction scheme.…”

Section: Discussionmentioning

confidence: 99%

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Huang

Ponomarenko

Wiederrecht

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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High-resolution mapping of cofactor-specific photochemistry in photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides was achieved by polarization selective ultrafast spectroscopy in single crystals at cryogenic temperature. By exploiting the fixed orientation of cofactors within crystals, we isolated a single transition within the multicofactor manifold, and elucidated the sitespecific photochemical functions of the cofactors associated with the symmetry-related active A and inactive B branches. Transient spectra associated with the initial excited states were found to involve a set of cofactors that differ depending upon whether the monomeric bacteriochlorophylls, BChl A , BChl B , or the special pair bacteriochlorophyll dimer, P, was chosen for excitation. Proceeding from these initial excited states, characteristic photochemical functions were resolved. Specifically, our measurements provide direct evidence for an alternative charge separation pathway initiated by excitation of BChl A that does not involve P*. Conversely, the initial excited state produced by excitation of BChl B was found to decay by energy transfer to P. A clear sequential kinetic resolution of BChl A and the A-side bacteriopheophytin, BPh A , in the electron transfer proceeding from P* was achieved. These experiments demonstrate the opportunity to resolve photochemical function of individual cofactors within the multicofactor RC complexes using single crystal spectroscopy.photosynthesis | transient absorption | light-harvesting

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Section: Discussionmentioning

confidence: 99%

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Huang

Ponomarenko

Wiederrecht

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…The LH2 complexes surround the RC-LH1 complexes in a two-dimensional network and serve as antennas for light harvesting [1,2,7]. Upon optical excitation, the energy is efficiently transferred from LH2 via LH1 to the RC, where it is used to initiate a cyclic electron transfer chain [8,9].…”

Section: Introductionmentioning

confidence: 99%

Contribution of low-temperature single-molecule techniques to structural issues of pigment–protein complexes from photosynthetic purple bacteria

Löhner

Cogdell

Köhler

2018

J. R. Soc. Interface.

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As the electronic energies of the chromophores in a pigment–protein complex are imposed by the geometrical structure of the protein, this allows the spectral information obtained to be compared with predictions derived from structural models. Thereby, the single-molecule approach is particularly suited for the elucidation of specific, distinctive spectral features that are key for a particular model structure, and that would not be observable in ensemble-averaged spectra due to the heterogeneity of the biological objects. In this concise review, we illustrate with the example of the light-harvesting complexes from photosynthetic purple bacteria how results from low-temperature single-molecule spectroscopy can be used to discriminate between different structural models. Thereby the low-temperature approach provides two advantages: (i) owing to the negligible photobleaching, very long observation times become possible, and more importantly, (ii) at cryogenic temperatures, vibrational degrees of freedom are frozen out, leading to sharper spectral features and in turn to better resolved spectra.

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“…24−31 From these studies it is well established that in the RC the absorbed photon-energy is used to drive a series of electron transfer reactions until the secondary ubiquinone (Q B ) has been fully reduced to Q B H 2 ; see Figure 1. 32,33 The dynamics of the energy transfer between the LH1 and the RC has been the subject of countless studies, and the characteristic time constants that have been found range from several picoseconds up to a few nanoseconds. 34−45 In some studies the fluorescent transients were described by up to five decay times that could not always be attributed to distinct processes.…”

Section: ■ Introductionmentioning

confidence: 99%

The Open, the Closed, and the Empty: Time-Resolved Fluorescence Spectroscopy and Computational Analysis of RC-LH1 Complexes from Rhodopseudomonas palustris

et al. 2015

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ABSTRACT:We studied the time-resolved fluorescence of isolated RC-LH1 complexes from Rhodopseudomonas palustris as a function of the photon fluence and the repetition rate of the excitation laser. Both parameters were varied systematically over 3 orders of magnitude. On the basis of a microstate description we developed a quantitative model for RC-LH1 and obtained very good agreement between experiments and elaborate simulations based on a global master equation approach. The model allows us to predict the relative population of RC-LH1 complexes with the special pair in the neutral state or in the oxidized state P + and those complexes that lack a reaction center. ■ INTRODUCTIONPhotosynthetic purple bacteria have evolved a wonderful modular principle for the light-harvesting (LH) apparatus that captures the solar radiation. These modules consist of pairs of hydrophobic, low molecular weight polypeptides that noncovalently bind a small number of bacteriochlorophyll (Bchl a) and carotenoid (Car) molecules and that self-assemble to produce the native pigment−protein complexes. 1−6 Most purple bacteria have two main types of complexes, the core complex, RC-LH1, and the peripheral complex, LH2. In the photosynthetic membrane the LH2 complexes are arranged in a two-dimensional network around the perimeter of the RC-LH1 complexes and the light energy absorbed by LH2 is transferred via LH1 to the reaction center (RC) where it is used to separate charge across the membrane. 7 For many years, high-resolution structural information has been available for the RC, 8−11 and the peripheral light-harvesting complexes 1−3 for a couple of species, whereas the first higher-resolution X-ray structure for a RC-LH1 complex has been determined only recently. 6 The current view is that there are at least two distinct classes of RC-LH1 complexes: Those that are monomeric, i.e., consisting of one RC surrounded by one LH1 complex, and those that are dimeric. 12,13 For RC-LH1 from Rps. palustris exists a lowresolution X-ray structure. 4 Accordingly, the RC is enclosed by an overall elliptically shaped LH1 consisting of 15 αβ-subunits that feature a gap, which is also consistent with data from optical single-molecule experiments. 14,15 Each subunit accommodates two light harvesting BChl a molecules giving rise to an absorption band at 875 nm. The reaction center complex accommodates a BChl a dimer (special pair, primary donor, P), two accessory BChl a molecules (B A , B B ), two bacteriopheophytin a (BPheo a) molecules (H A , H B ), and two ubiquinones (Q A , Q B ) bound to two protein subunits denoted L and M. The cofactors are arranged in two nearly identical branches, called A and B, which share the primary donor, P. 9,11,16,17 In particular the RC from Rhodobacter (Rb.) sphaeroides has served as a cornerstone for elucidating structure−function relationships employing a large variety of spin resonance 18−23 and optical spectroscopies. 24−31 From these studies it is well established that in the RC the absorbed photon-energy is used to dri...

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The First Picoseconds in Bacterial Photosynthesis—Ultrafast Electron Transfer for the Efficient Conversion of Light Energy

Cited by 190 publications

References 132 publications

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Contribution of low-temperature single-molecule techniques to structural issues of pigment–protein complexes from photosynthetic purple bacteria

The Open, the Closed, and the Empty: Time-Resolved Fluorescence Spectroscopy and Computational Analysis of RC-LH1 Complexes from Rhodopseudomonas palustris

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